Saturday, August 13, 2011

Laboratory diagnosis of adenovirus

• Collection of specimens and virus isolation
Collection of specimens is needed as early as possible to optimize viral isolation and to detect adenovirus Ag or nucleic acid directly in clinical samples. The duration of excretion of Adenoviruses at the time of acute infection is about 1 - 3 days from throat, nose, stool, and eye from patients with pharyngoconjunctival fever. However, after the acute period, adenoviruses may be latent in some tissues, such as the tonsils, or may be reisolated intermittently from throat or stool cultures for periods of months to years after primary infection in some patients (Hierholzer et al., 1993).
• Antigen detection
Adenoviruses have a common group Ag that is detected by EIA and CF (Nauschuetz, 2000).
• Serology
Type-specific monoclonal (MAbs) that could be used in the IF, ELISA and latex agglutination procedures are currently used for differentiating adenovirus Ad40 and Ad41 from other adenoviruses in the feces. Specific serotyping includes use of MAbs to type-specific epitopes on hexon. In current practice for specific adenovirus serotyping, HA properties of a virus isolate are determined, followed by serologic tests to inhibit HA or to neutralize the virus with type-specific Abs. Agents preliminarily characterized as adenoviruses are tested for their ability to hemagglutinate rhesus or rat cells. Further HA testing using human cells can provide supplemental information (Lukashok and Horwitz, 1998).
Serology is less useful in acute clinical setting. If serologic diagnosis is pursued, serum should be obtained as early as possible in the clinical course, followed by a second titer 2-4 weeks later. A 4-fold rise in acute titers to convalescent titers is diagnostic (Gompf and Oehler, 2007).
• Nucleic acid detection
PCR is most sensitive technique for detection of adenovirus using primers based on base sequences that are common to the genus (Echavarria et al., 1998). Current developments are using Real- time PCR to obtain more semi quantitative data